The invention relates to a device for cutting shock damping of work machines, in particular for presses and stamping or nibbling machines, and to a method for cutting shock damping. The invention is employed in work machines which have a machine frame and a working drive for moving a working tool along a working direction, and in which the machine frame is deformed elastically by a working force exerted by the working drive for machining a workpiece, the working drive providing a control variable for determining the working force.
In machining, for example stamping, of a fixed workpiece, forces varying sharply in time occur between the working tool and machine frame and, in particular, may also change abruptly. In this case, a distinction can be made in a simplified way between a pressure build-up phase and a cutting breakthrough phase. During the pressure build-up phase, the working tool lies on the workpiece and an increased working force is built up by means of the working drive. The machine frame absorbs the working force exerted by the working drive upon the workpiece, since the workpiece provides a counterforce corresponding to the working force. In this case, the machine frame is deformed elastically to a certain extent. In particular, expansion of the machine frame along the direction of the working force of the working drive takes place. During the pressure build-up phase, comparatively high energy may therefore be stored in the elastic deformation of the machine frame.
At the moment of the cutting breakthrough, the workpiece yields abruptly to the working tool. The counterforce provided by the workpiece consequently ceases suddenly, thus leading to a correspondingly abrupt detensioning of the elastically deformed machine frame. Elastic reforming therefore occurs during detensioning, typically within fractions of a millisecond. The stored energy is released partially in the form of sound waves, thus leading to noise generation designated as “cutting shock”.
Due to the sudden reforming, the work machines, in particular the machine frame and mounted functional elements, are subjected to a particularly increased load. This, on the one hand, may shorten the useful life of the work machine and, on the other hand, have an adverse effect upon the machining quality of the workpiece.
For damping the undesirable cutting shock, in particular, devices with hydraulic damping cylinders have become known. Thus, for example, DE 10 2005 053350 A1 shows a controllable supporting arrangement for generating a variable force between a ram and a press platen of a press. The supporting arrangement is in this case controlled as a function of the position of the ram. The device is then set to the workpiece to be machined so that, at the moment of the cutting breakthrough, the supporting arrangement absorbs the working force of the ram. This solution requires a technically complicated sensor arrangement for detecting the ram position and makes it necessary to calibrate the supporting arrangement for different materials and different geometric dimensions of the workpiece to be machined.